An activated-carbon-fiber hemoperfusion device was developed by Southern Research Institute for treatment of uremia and drug overdose. The activated carbon is encapsulated in water-swollen fibers of hydroxyethylcellulose, which protect the blood from direct contact with the carbon but allow solutes in the blood to be adsorbed. As shown by experiments in vitro and in vivo, the encapsulated carbon removes a variety of drugs and other solutes from blood. However, the present device is too large for treatment of small children or experimental animals. We have miniaturized the hemoperfusion device and studied some of its mass-transfer characteristics. We will evaluate the small device with dogs as test animals to determine its ability to remove blood specific toxic substances that are frequently associated with accidental poisoning of children.